The analysis of ions in space has been conducted principally by use of electrostatic analyzers or by mass spectrometers. The former measures the ion energy per unit charge (proportional to mv.sup.2 /q, where m is mass, v is velocity, and q is charge), while the latter measures m/q in cases in which the velocity is either negligible or assumed to be known. Some space projects require an instrument which can unambiguously measure ion m/q, energy, and direction with as high an efficiency and speed as possible over a wide energy range and angular field of view.
In recent years, energetic ion mass spectrometers have been developed which have a magnetic analyzer in front of or behind an electrostatic analyzer. Most analyzers of this type have only a single sensor. Only ions with a particular m/q, v, and direction can pass through the analyzers to the detector at any one time. The ion population is studied by varying the voltage on the electrostatic analyzer as well as an accelerating voltage, and by pointing the instrument in different directions at different times. Other ion spectrometers have been built which use an electric (or magnetic) field to spread out a beam of ions which has been preselected by a magnetic (or electric) analyzer. The dispersed beam can be sensed with a line of detectors, with each element in the line corresponding to a fixed value of m/q. These instruments must also be pivoted in two dimensions to detect ions over a wide solid angle, to obtain directional information, and scanned in voltage to measure the ion energy.
An ion mass spectrometer that could analyze ions received over a wide range of angles and which could simultaneously determine each ion's angle, m/q, and energy, would be of considerable value in space research.
It is desireable to measure rapidly four properties or parameters of ions--namely the mass charge ratio, the energy, the elevation angle, and the azimuth angle. With a single sensor, one must scan through each of these four parameters sequentially in time. With a line of detectors, one parameter can be measured continually while the other three are sequenced. The invention described herein has the capability of measuring two properties continuously on a two dimensional sensor, so only two remaining properties need to be measured on a time-shared basis.